The inventor has worked in the field of safety in the workplace for some twenty-five years and has performed considerable work on safety studies dealing with offshore drilling and production platforms. His studies have determined that one of the major causes of injury, particularly spinal injury, results from workmen entering or leaving stationary platforms to enter or leave a workboat. Because of the swells in the open ocean, the workboats cannot tie directly to the stationery platform structure and move up and down in the swells causing a serious problem for personnel who need to move between a platform and a workboat.
In rough seas it is not uncommon for the boat to be positioned eight or more feet from the platform. Because of the pitching of the boat (normally three to five feet of vertical movement) a workman may slip or land improperly on the boat or platform, causing disabling injuries.
The accepted (and archaic method) to transfer a workman from a workboat to a platform employs a "Swing Rope" (see FIG. 1). The swing rope is suspended from the upper deck of a platform and extends past the landing platform that is located several feet above mean sea level. The rope will often touch the sea at mean tide and be several feet above the sea at low tide. The swing ropes each have a series of knots, to stop a users hand from slipping, spaced about several feet apart. The use of the rope varies depending on the relative position of the user.
If the user is on the platform, the user judges the mean height of the work boat above or below the platform and grabs the rope at the appropriate knot. (The actual technique is difficult to describe, should be explained by a video, and must be experienced by a person to fully understand the method. After one's first experience, one will still be terrified!) The user then swings out over the water, over the boat, moves the hands over knots--if necessary, slides down the rope, lets go, and drops on the deck of the boat.
Timing of the drop is critical; the user should swing out from the platform and let go of the rope just as the boat is falling away from the platform due to wave motion. Injury will occur, if the workman mis-times and drops, as the boat is moving upward. NOTE--mis-timing can be handled by simply returning to the platform. Transfer from platform to boat is difficult, but certainly easier than transfer from boat to platform.
If the user is on the boat, the boatman uses a boat hook to grab the rope. The user holds onto the rope. Now the user must judge the maximum point of upward motion of the boat, grab the rope and swing to the platform. It is absolutely essential that the swing not be attempted until the boat is at the maximum upward point of travel. (This patent attorney has often arrived on his back sliding along the landing area of the platform due to misjudgment of upward travel.) The real danger in this operation is caused by pure misjudgment. If misjudgment occurs, the "swinger" returns to the boat, which may be coming up and hit the person on the rope. BUT, worse, the "swinger" might be caught between the boat and the platform--death or severe injury will occur!
At present the only other means of safety entering or leaving a platform is by gangway, helicopter or by a man-basket that is operated by a pedestal crane. In the case of a man-basket, usually the crane operator is unable to visualize the man-basket as it is lowered below the main platform, which may be seventy-five feet above the water surface. A flagman must attempt to direct the lowering of the man-basket onto the workboat. At times the man-basket is dropped onto the boat deck with such force that the transferring workmen are injured. It is very difficult to synchronize the man-basket movement with the vertical movement of the boat because of the lag in communication between the crane operator and the flagman.
The prior varies from gangplanks or gangways, through man-basket systems, to complex elevator systems that require special attachment points on the workboat. The first offshore oil production occurred in about 1948 in shallow water just offshore from Louisiana. As production pushed further offshore the problems of a swig rope became more apparent and the prior art--for offshore platforms--essentially started at that time. Pitts et al., U.S. Pat. No. 2,641,785, disclose a Marine Transfer Ramp, which is designed to couple into an attachment point on a boat. It is interesting to note that the inventors worked for an oil company and the application was filed in 1948. Winfrey et al., U.S. Pat. No. 3,064,829, disclose a marine Transfer System, which is essentially an elevator system employing counterweights and a special attachment point on the boat. Mizzel, U.S. Pat. No. 3,426,719 discloses a Marine Transfer Device, which is essentially a hydraulically controlled gangway designed to couple onto a boat. Mizzel is but one of many gangway or gangplank devices. These devices, although useful, are expensive and have not found use, except during the construction phase, on offshore platforms. Williams, U.S. Pat. No. 4,590,634, discloses a Marine Transfer Device, which is similar to that of Mizzel except that a platform based crane is used to operate and position the gangway onto a workboat.
True et al., U.S. Pat. No. 2,876,919 disclose a marine Transfer Device, which is designed to interactively couple between a platform and a workboat. The device requires special equipment on both the workboat and the platform. The equipment is complex and would be expensive to install on every platform. Walker, U.S. Pat. No. 2,963,178, discloses a Marine Landing Assembly, which is another elevator type system designed to attach to the platform and move personnel and equipment between a boat and the platform.
Other variations of the gangway system may be found in the disclosures by Anders, U.S. Pat. No. 4,601,253 and Smedal, U.S. Pat. No. 4,369,538. Anders discloses an Offshore Boarding Apparatus, which is a ladder device operated from the platform. Smedal discloses an Apparatus for Transfer of Persons and Goods between Structures Offshore, which is a tubular bellows like gangway operated from the platform and requires special attachment points on the workboat.
Kanady et al., U.S. Pat. No. 2,963,179, disclose a Marine Transfer Assembly, which is based about a floating boat ramp into which the workboat latches. The ramp is lowered from the platform by a winch/crane.
Some prior art may be found in escape systems for offshore platforms. These systems are really designed to allow personnel to leave the platform under emergency conditions and would not allow for dual egress. Aanensen, U.S. Pat. No. 4,602,697, discloses an Escape Means for Sea-Based Construction, which is a gangway device, operated from the platform that terminates in a rubber slide.
The prior art then turns to man baskets or cages, which may be controlled from the platform. Rees, Jr., U.S. Pat. No. 2,874,855, discloses a Personnel or Object Transfer apparatus and Method, which is essentially a man basket operated from the platform. The man basket moves up and down about a guide cable. The guide cable attaches to a point on the boat and moves with the boat motion. An operator is required on the platform.
Stair, U.S. Pat. No. 4,180,362, discloses a System to Transfer Cargo or Passengers . . . The system uses a man-basket controlled from the platform that interacts with a constant tension winch on the workboat. Although the system will allow for the safe transfer of men and materials, an operator is required on the platform and a complex system must be installed on both the workboat and the platform. MacDonald et al., U.S. Pat. No. 4,395,178, disclose a Transfer System for Use between Platforms . . . , which is a modification of Stair. MacDonald requires similar special equipment on both platform and workboat and operators at both sites.
Kimon et al., U.S. Pat. No. 4,412,598, disclose a Personnel Transfer Apparatus and Method, which uses a man-basket operated from the larger object. The larger object is a ship, although the device could be used on a platform. Again an operator is required on the platform. The base disclosure goes to an apparatus and method for balancing the vertical motion of the man-basket while in contact with the workboat (or tender).
Peyre et al., U.S. Pat. No. 4,630,542, disclose a Nacelle, which may be used to transfer men and equipment between a platform and a workboat. The device is somewhat complex and requires a crane (and operator) on the platform. The nacelle is internally powered and couples itself about a cable attached between the crane hook and the workboat. An internal hydraulic tensioner, within the nacelle, takes up the relative motion between the workboat and the platform. There is a limit to the amount of relative motion that may be absorbed by the device, and in rough seas the device would be limited. Strong et al., U.S. Pat. No. 5,713,710, disclose a Transfer System, which is similar to Peyre, except that there is no hydraulic tensioner to absorb relative motion and all control rests in the platform crane operator. Relative motion between the platform and the workboat is absorbed by a "bungee cord."
Finally, the prior art contains two interesting devices. Henderson, U.S. Pat. No. 4,166,517, discloses a Pilot's Power Elevator, and Peyre, U.S. Pat. No. 4,739,721, discloses a Boat for Vertical and Horizontal Transfer. Henderson solves the transfer of a pilot between a pilot boat and the ship using an elevator system operated from the ship. Peyre, on the other hand, proposes a self-powered miniature boat that may raise and lower itself from a larger vessel or a platform to a workboat or the water. However, attachment to the platform requires an operator on to the platform.
All of the prior art requires an operator on the platform to which egress is required by personnel (and materials) on the workboat. Very often the seas are too rough to use either the Swing Rope or crane to transfer men from the boat. This presents a serious maintenance problem since many platforms require daily visits by a production worker. In daily operations, men and equipment are transferred between platforms that (in the vast majority) have no personnel in residence; thus, there are no operators available to make the initial transfer between vessel and platform. It should also be noted that at the end of working day, nobody could be left on the platform to operate any egress equipment. Finally and based on the inventor's experience, a system that uses off-the-shelf devices is required.
Therefore and because of the need for a dependable and safe method of transferring workmen from the boat to the platform without the need for operators on the platform, the instant invention was developed. At present, there are about 4,000 platforms operating in the Gulf of Mexico. Each of these platforms needs an effective and safe personnel transfer system. Worldwide there are some 100,000 platforms.